Sunscreen formulations for use on human skin are well known, and many different types are commercially available to satisfy diverse consumer needs. For example, sunscreen formulations having different sun protection factor (SPF) values are available, thus allowing consumers to choose the amount of protection desired. SPF values range from zero upward with higher values indicating greater amounts of sun protection. SPF values of 2-4 indicate minimal sun protection, 4-6 indicate moderate sun protection, 8-15 indicate maximal sun protection, and above 15 indicate ultra sun protection.
One important consideration when choosing a sunscreen is whether it resists coming off in water. "Water resistant" formulations can undergo about 40 minutes in water without significant SPF loss, whereas "waterproof" formulations can undergo about 80 minutes in water without significant SPF loss. Waterproof formulations can be especially desirable because they eliminate the need for reapplication after swimming, bathing or excessive perspiration.
Other considerations can also be important when choosing a sunscreen product. For example, certain individuals are allergic to sunscreen compositions that contain p-aminobenzoic acid (PABA) or derivatives thereof, which are especially prevalent in higher SPF formulations. Furthermore, PABA and derivatives thereof cause stains which may be especially problematic and irritating to boat owners.
Thus, it obviously would be desirable to formulate waterproof sunscreen compositions, some of which do not contain PABA.
Certain UV A sunscreen agents such as 2-hydroxy-4-methoxybenzophenone, commonly referred to as benzophenone-3 or oxybenzone, are often used in conjunction with UV B type sunscreen agents to effect a broader spectrum of sunscreen protection. Benzophenone-3 absorbs ultraviolet rays in the higher UV A range of about 3200-4000 Angstrom wavelengths, whereas UV B sunscreen agents such as PABA absorb ultraviolet rays in the more harmful and burning 2800-3200 Angstrom wavelength range. Benzophenone-3 is often difficult to solublize and keep in solution, especially in the presence of water. It is more soluble in PABA esters such as octyl dimethyl PABA then it is in water or alcohol. Higher concentrations of benzophenone-3 (up to about 6% by weight) are desirable when formulating sunscreens having higher SPF values. Heretofore, however, it has been difficult to achieve stable concentrations containing benzophenone-3 at concentrations greater than about 3%. In fact, some products having higher concentrations maintain the benzophenone-3 in suspension rather than in solution.
A second problem confronted when formulating waterproof sunscreens is providing acceptable consistency, skin-feel and stability to the product. Those factors, which are important to achieving consistent distribution on the skin, even sun protection, consumer acceptance, and commercial viability, are largely functions of the vehicle which carries the sunscreen agents.
For the above reasons, it would clearly be desirable to formulate a pharmaceutical vehicle capable of providing acceptable consistency, skin-feel and stability, and which is also capable of solubilizing higher concentrations of benzophenone-3 and/or other sunscreen agents.
With that in mind, we investigated the use of copolymers of polyvinylpyrrolidone (PVP) and long alkyl chain olefins, more commonly known as alkylated PVP's. Such copolymers have been produced for over twenty years by GAF Corporation, 1461 Alps Road, Wayne, New Jersey, under the tradename Ganex resins. Ganex resins were chosen because they are known to impart waterproof and moisture barrier properties to various skin care products, including sunscreens. To date, however, no Ganex-containing compositions have been produced that can satisfactorily solubilize benzophenone-3 (especially in higher concentrations) to produce a sunscreen having acceptable consistency, skin-feel and stability.
It has now been discovered, that high oil phase waterproof pharmaceutical vehicles comprising Ganex resins and the unique solvent systems disclosed herein possess an unexpectedly superior ability to solubilize sunscreen agents, including concentrations up to about 6% by weight of benzophenone-3. Furthermore, it has been found that the pharmaceutical vehicles themselves play a significant part in determining SPF values, and in some cases, can contribute to a very high final waterproof SPF values that others cannot achieve.
All of the weight percentages listed herein are weight percentages based upon the total weight of the pharmaceutical vehicle or sunscreen formulation.